EP0908709A2 - Device for contactless vibration measurement - Google Patents

Abstract

The invention relates to a device for optically measuring an object (13), in particular for measuring displacement and / or vibration. It has a device (5, 6, 17) for displacing the measuring beam approximately in parallel. <IMAGE>

Description

The invention relates to a device for the optical measurement of a Object, in particular for displacement and / or vibration measurement, by means of a laser interferometer, the measuring beam in the beam path of a Microscope is coupled, the device being a device for has approximately parallel displacement of the measuring beam.

Laser interferometers represent ideal measuring arrangements for high-resolution Path or vibration measurements. The measurements are pure optically, so contactless instead. They are therefore particularly suitable for micromechanical, microelectronic or microbiological objects, where the attachment of z. B. for other Schwinginngsmeßverfahren usual acceleration sensors because of the low mass of the Object by itself.

When measuring such small objects, it is desirable observe the area to be measured in a microscope and the To be able to position the measuring point with the aid of the microscope. There is one Arrangement known, in which a measuring beam over the illumination path in the beam path of the microscope is coupled. Because of the coupling geometric conditions to be observed via the lighting path can interferometer and microscope only as related Unit run. The use of this device is therefore high Production costs counter because always in addition to the interferometer a special microscope must also be manufactured, which, in particular regarding the construction of its lighting path, the one used Interferometer is to be adjusted.

Laser interferometer microscope for the messurement of nanometer vibrational displacements of a light-scattering microscopic object" von Netten in Acoust. Soc. Am. 83 (4), April 1988, S. 1667 - 1074. Bei dieser Meßvorrichtung wird mit zwei Laserstrahlen gearbeitet, die auf dem Meßobjekt interferieren. Bewegungen des Meßobjektes können nur senkrecht zur Beobachtungsrichtung (In-Plane) gemessen werden.The preamble of claim 1 is based on the first publication

Laser interferometer microscope for the messurement of nanometer vibrational displacements of a light-scattering microscopic object "by Netten in Acoust. Soc. Am. 83 (4), April 1988, pp. 1667-1074. Two laser beams are used in this measuring device, which interfere with the measuring object Movements of the measuring object can only be measured perpendicular to the direction of observation (in-plane).

Based on this, the object of the present invention is a device for non-contact displacement and / or vibration measurement specify an easier and more accurate measurement of individual Object points and the analysis of larger object areas allows. Farther is a device for non-contact displacement and / or vibration measurement be made available on standard microscopes can be used without extensive conversion work.

This object is achieved in that the coupling of the measuring beam via a camera connection (C-mount) of the microscope takes place that said displacement means a displacement of Measuring beam impact point on the object to be measured and that the measuring beam reflected or scattered back from the measurement object automatically via the camera connection from the beam path of the microscope uncoupled and returned to the measuring system.

The invention is based on the following findings: interferometers not coupled with a microscope is one Angle adjustment of the measuring beam is common to several, side by side To be able to record measuring points. This would be in a microscope lead to considerable difficulties. To with the measuring beam to always hit through the lens would have the point to which the measuring beam would have to be swiveled inside the microscope to lie. This point should be absolutely precise under all circumstances become. This would possibly be on circular orbits outside of the microscope, extremely precise and therefore very complex Swivel mechanics require, if it could be realized at all. An installation of such a mechanism in different microscopes would be not possible because the pivot point depends on the geometry of the microscope should have a different location.

Due to the parallel displacement of the measuring beam according to the invention, it becomes possible not only one, but several points of the measuring object Detect without moving the object to be measured, the equipment complexity for shifting the measuring beam is comparatively small

By coupling the measuring beam over the camera connection (C-mount) of the microscope, it runs through practically the entire microscope optics with the exception of the eyepiece, which makes the measurement considerably more precise can be executed than in the known case.

This also has the advantage that the measuring device is universal can be used on different microscopes because the mentioned camera connections for photo or video cameras as standard are available on most commercially available microscopes in which Usually even with standardized connection dimensions. You can find the same everywhere optical and mechanical connection conditions. This is not the case only for the size of the connector, but also for the fact that the microscope optics the light coming from the measurement object in a defined Focused just behind the end of the camera connector, namely, where there is a video camera, if installed the CCD chip is located.

The light scattered by the object is preferably transmitted via the same light path, how the transmitted light is fed back into the interferometer and interferes there with the reference beam. Only such movements are involved of the object to be measured in the direction of the measuring beam run (out-of-plane). This often gives advantages in terms of the positioning of the measuring device relative to the measurement object.

The displacement device advantageously allows a point and / or line-by-line optical scanning (scanning) of the measurement object in any Direction, expediently in the x and y directions. To do this, the measuring beam is either shifted by hand in parallel or its shift will be automatic made, for example, under the control of a computer.

The shifting device has for shifting the measuring beam in parallel a lens that can be displaced laterally approximately perpendicular to the beam path. There this lens has a very low mass, it can be very quickly and move precisely, which enables effective and precise scanning.

Instead of using a lens, the beam can be shifted in parallel also by several corresponding, pivotable and possibly detachable mirrors are made.

To adjust the displacement device are necessary because of the small Adjustment paths advantageous micrometer screws, piezo elements or the like used. Piezo elements can also be very easily attached to a automatic control connect to the scanning process for the user to simplify.

To couple the measuring beam, it is expedient to use a Focused focal plane (intermediate image plane) of the microscope. This can the device has a focusing lens. From this focal plane the focused measuring beam is then through the optics of the microscope the measurement object is shown.

The beam feed to the displacement device is simple and advantageously by means of an optical waveguide, for example in the form of a glass fiber optic, realize. From the end of the optical waveguide on the microscope side is the one mentioned Focusing lens arranged at a distance equal to its focal length corresponds. Due to the arrangement described, the point on the Measuring beam is focused in the focal plane by moving the displaceable Lens can be moved laterally in two axes.

It is particularly advantageous if you look at the object at the same time and can measure. For this purpose, the measuring beam is in via a beam splitter Form of a partially transparent mirror or optical edge filter coupled. This beam splitter is expediently arranged in a housing, the at least one connector for the microscope, one connector for a camera and a connection for coupling the measuring beam having.

The measuring beam is directed onto the axis of the Beam path of the microscope swiveled. On the other hand, the partially permeable Mirror light from the test object to a video camera, so that you can look at the object. If the mirror also one Part of the measuring beam reflected by the object reaches the video camera then the measuring point is also shown in the video image. Of course this arrangement can also be carried out in reverse, so that the measuring beam passes the mirror while the normal Light reflected from the measuring object from the partially transparent mirror to the camera becomes.

The partially transparent mirror is advantageously characterized by a frequency selective reflexivity. It also has a high transmission for visible light (450 nm - 550 nm), but a small one in terms of Measuring beam (633 nm). Values of 80% transmission are advantageous for visible light and 0.2% for the measuring beam.

Since the camera is no longer in through the interposed beam splitter the focal plane of the microscope intended for them can, more lenses are provided here to the microscope image in the Map camera.

Figur 1

eine schematische Darstellung des Strahlengangs und der optischen Elemente eines Mikroskops mit einer aufgesetzten Vorrichtung zur optischen Vermessung;

Figur 2

eine Verschiebeeinrichtung einer Vorrichtung nach Figur 1; und

Figur 3

ein Ausführungsbeispiel einer Verschiebemechanik der Verschiebeeinrichtung nach Figur 2.

Further features and details essential to the invention result from the description of an exemplary embodiment with reference to the drawing; shows

Figure 1

a schematic representation of the beam path and the optical elements of a microscope with an attached device for optical measurement;

Figure 2

a displacement device of a device according to Figure 1; and

Figure 3

an embodiment of a displacement mechanism of the displacement device according to Figure 2.

In FIG. 1, a measurement object can be seen on the stage of a microscope 3 13. The object 13 is a lamp unit built into the microscope 12 via a microscope beam splitter 11 through the objective 10 of the microscope 3 illuminated. The light reflected by the object 13 becomes from the objective 10 and, if appropriate, a microscope colimator lens 9 in the eyepiece of the microscope or on the focal plane (intermediate image plane) 7 of a camera connection 7a of the microscope. It happens it in turn the microscope beam splitter 11 of the illumination device. The camera connection 7a is located on the top of the microscope 3 approximately vertically above object 13.

In the drawing, a laser interferometer 1 is shown at the top right shown, which is usually placed next to the microscope. Here it is preferably a so-called heterodyne interferometer with an optical frequency shift of the measuring beam the reference beam, which ensures that the Object speed is possible. Such an interferometer is e.g. B. from known from DE 44 24 900 A1, to which reference is hereby made in full becomes.

A light beam is emitted from the laser interferometer 1 by means of a light guide 2 led to the microscope in the form of a fiber optic connection. The Light that emerges from the output end 4 of the fiber is with the help of a Kolimator lens 5 summarized in parallel. A focusing lens 6 focuses the collimated beam into the focal plane 7 of the microscope.

It is essential that the device is a device for approximately parallel Moving the light beam has. In the illustrated embodiment contains this shifting device the Kolimatorlinse 5, the Focusing lens 6 and the slide mechanism shown in Figures 2 and 3 17th

The principle of parallel displacement can be seen particularly well in FIG. 2 remove. There, the colimator lens 5 is approximately perpendicular to the optical one Axis slidable and shown in an upper and a lower position. In this case, the light emerging from the fiber end 4 is turned on a parallel bundle of rays a or b and passes under one Angle relative to the optical axis to the focusing lens 6. This Angle relative to the optical axis depends on the position of the colimator lens 5 from. It can be moved laterally by moving the colimator lens 5 using the slide mechanism 17. In Figure 2 is like this instead of the beam a after moving the Kolimatorlinsel 5 that Beams b forwarded to the focusing lens 6.

Through the focusing lens 6, the incoming parallel beam, so z. B. a or b, focused and on the focal plane 7 of the Microscope pictured. This focal plane is in Figure 2 compared to Figure 1 shown rotated by 90 ° to make crossing difficult to avoid the two illustrated beam bundles a and b.

By moving the Kolimatorlinsen 5 perpendicular to the optical axis This results in an angular adjustment of the parallel behind this lens Beam through the focusing lens 6 in a parallel shift is converted. Beams a and b run behind lens 6 parallel to each other, but shifted against each other.

Regarding the angle adjustment taking place in front of the focusing lens 6 the fiber end 4 the tipping point. That is why it is exactly in the distance of the To arrange the focal length of the focusing lens 6. On the other hand, must the focusing lens 6 for focusing the beam also around its focal length be away from the focal plane 7 of the microscope.

The displacement mechanism 17 with which the colimator lens 5 is displaced is shown in Figure 3. By operating one of their two main adjusters 17a is pushed in each case by means of an inner displacement element 17b a bevel shaft 17c against a bevel shaft return spring 17d. The bevel shaft presses on one or more cylinder pins 17e, the movement convert the bevel shaft 17c into an orthogonal movement and on transmit an approximately square holder block for the lens 5. This The holder block is placed on the cylinder pins 17e opposite each other Sides supported by holder block return springs 17f. These will when the main adjuster 17a is screwed in by the described mechanism compressed so that there is a lateral displacement of the Lens 5 results in the direction away from the main adjuster. Conversely, the Unscrew one of the main adjusters 17a through the lens 5 Holder block return spring 17f laterally towards the main adjuster 17a postponed. Due to the orthogonal arrangement of two main adjusters the lens 5 can be moved in any plane in one plane.

At this point it should be noted that in addition to the one shown mechanical adjustment via micrometer screws also an electromechanical with piezo elements is conceivable. In principle, it can be analog can be built up by placing piezo elements at the positions of the cylinder pins 17e can be set. These then press depending on the electrical applied Apply more or less tension to the holder block and generate such a corresponding mechanical displacement of the Kolimatorlinse 5. The control voltages of the piezo elements can be advantageously over generate control electronics connected to a logic processor can be a computer-assisted displacement of the Kolimatorlinsen 5 and thus to enable the measuring beam. So you can 13 quickly and easily on many, e.g. B. arranged side by side on a grid Measure points.

To explain the measurement process, reference is again made to FIG. 1. The measuring beam is from the fiber end 4 via the Kolimator- 5 and focusing lens 6 on the focal plane 7 of the microscope in the manner described shown, or move parallel to this focal plane. He is deflected by a beam splitter 8, the simultaneous Use of an observation camera 16 enables and described below becomes. As with most microscopes, the embodiment from the focal plane 7 of the microscope the measuring beam via the optics of the microscope, that is microscope colimator lens 9, microscope beam splitter 11 and objective 10 mapped onto the measurement object. A parallel shift of the measuring beam in the focal plane 7 also produces a parallel one Moving the measuring point mapped onto the measuring object 13. Indeed is this shifting and also the size of the measuring point reduced accordingly by microscope optics.

The measurement beam is reflected back by the measurement object 13 and is imaged again in the interferometer by the optical arrangement described. A shift of the lens 5 always shifts the transmitter and receiver at the same time.

Now the measuring object 13 moves in the direction of the measuring beam, for example due to vibrations, or is it at different measuring points different heights, this is expressed in a change in the optical Path length of the measuring arm (path length of the measuring beam to the object to be measured and back) of the interferometer. The changes accordingly Interference of measuring and reference beam in interferometer 1 and the triggering one Modification of the measurement object 13 can be done in the interferometer 1 in a known manner Be detected and measured precisely.

To realize the scanning of several measuring points without the measuring object 13 it is important to move the measuring beam in a focal plane of the microscope 3 focus and move it in parallel. Such Focal plane can be found standardized on the camera connection of numerous microscopes. A video camera is usually attached to this so-called C-mount connected, the CCD chip to lie in the focal plane 7 comes, so that the measurement object 13 is imaged directly on the chip. So can be measured object 13 instead of through the eyepiece of microscope 3 watch a video camera, the observation process if necessary can be recorded. This standardized camera connection 7a makes use of the invention by the device for optical Measurement of the measurement object 13 is constructed so that, and this it is essential that the measuring beam at the camera connection 7a of the microscope 3 in whose beam path is coupled. Thus, the same or even the same components and optical arrangements on different Find microscopes.

To measure the measurement object 13 using the interferometer 1 simultaneous observation by the video camera 16, for example for precise Positioning the measuring beam, the arrangement shown in Figure 1 is used. For this purpose, it has a beam splitter 8 with frequency-selective reflectivity. This has in the usually very narrow frequency range of the laser interferometer a very high reflectivity, so that from the fiber end 4 emerging measuring beam almost completely in the beam path of the microscope 3 is reflected. After reflection on the measurement object 13, the measurement beam again from the beam splitter 8 for the most part into the interferometer 1 reflected back, but about 0.2% of the measuring beam through the beam splitter 8 are transmitted through. This 0.2% of the measuring beam are visible in the image of the video camera 16, so that you can see can, at which point of the measurement object 13 is currently being measured. Next the high reflectivity in the range of the wavelength of the measuring beam, usually the 633 nm generated by a helium-neon laser the beam splitter 8 has a very low reflectivity in the visible range Light from approximately 450 nm to 550 nm. Accordingly, about 80% of visible light is transmitted, resulting in a bright image in the video camera 16.

Since the CCD chip of the video camera 16 in the described invention Arrangement no longer in the focal plane 7 of the microscope 3 is located, the light transmitted by the beam splitter 8 is by further Imaging lenses 14 and 15 in the video camera 16. This applies to both the visible light generated by the lamp unit 12 as well as for the transmitted part of the measuring beam of the laser interferometer 1. The Kolimatorlinse 5, the focusing lens 6, the beam splitter 8 and the other lenses 14 and 15 are expediently shown in a dash-dotted line Housing 20 arranged, the one at its lower end Standard corresponding connection, which simply to the C-Mount 7a common microscopes can be connected. The housing 20 has further connections for the light guide 2 of the interferometer 1, or its End 4 and 16 for a commercially available video camera.

Overall, the invention is characterized by the advantages that an accurate Positioning of the measuring point on the measuring object 13 can take place, without having to move the test object 13, that the test object can be measured by scanning and that for measurement necessary components on any commercially available microscope with camera connection be excluded without being changed or optically new need to be set up.

Claims (13)

Device for the optical measurement of an object (13), in particular for displacement and / or vibration measurement, by means of a laser interferometer (1), the measuring beam of which is coupled into the beam path of a microscope (3), the device comprising a device (5, 6 and 17) for approximately parallel displacement of the measuring beam,
characterized,
that the coupling of the measuring beam via a camera connection (7a) of the microscope (3) takes place, that said displacement device (5, 6 and 17) causes a displacement of the measuring beam impact point on the object to be measured (13) and that the Measurement object reflected or scattered back measurement beam is coupled out of the beam path of the microscope via the camera connection (7a). Device according to claim 1,
characterized,
that the laser beam is divided into a measuring beam and a reference beam and the measurement is carried out by superimposing both beams. Device according to claim 1,
characterized,
that the path and / or vibration measurement takes place in the direction of the measuring beam. Device according to claim 1,
characterized,
that the displacement device (5, 6 and 17) permits a point and / or line-by-line optical scanning of the measurement object (13). Device according to one of the preceding claims,
characterized,
that the displacement device (5, 6 and 17) has a lens (5) which can be displaced laterally approximately perpendicular to the beam path and in particular also has one or more mutually corresponding, pivotable and, if appropriate, removable plates or plane plates. Device according to one of the preceding claims,
characterized,
that the displacement device (5, 6 and 17) has actuators in the form of micrometer screws (17a), piezo elements or the like. Device according to claim 1,
characterized,
that the displacement device (5, 6 and 17) has a focusing lens (6) which focuses the measuring beam onto a focal plane (7) of the microscope (3). Device according to one of the preceding claims,
characterized,
that the beam is fed to the displacement device (5, 6 and 17) via an optical fiber (2). Device according to claims 7 and 8,
characterized,
that the focusing lens (6) is arranged at a distance from the light guide end (4) which corresponds to its focal length. Device according to claim 1,
characterized,
that the measurement beam is coupled in via a partially transmissive beam splitter (8), which in particular has a frequency-selective reflectivity. Apparatus according to claim 10,
characterized,
that the beam splitter (8) is arranged in a housing with at least one connection to the microscope (3), a connection for a camera (16) and a connection for coupling in the measurement beam. Device according to claim 1,
characterized,
that the displacement device (17) with its two lenses (5, 6) is installed in a housing (20) which has at least one connection to the microscope (3), a connection for the measuring beam of the interferometer (1) and optionally a connection for has a camera (16). Device according to claim 12,
characterized,
that the housing (20) also contains the beam splitter (8) and optionally at least one further lens (14, 15) for the camera connection.

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